The Ace Race Parts brand of metric Oxygen (O2) Sensor Bung Plugs are precision machined using 1018 Mild Steel and work with all standard O2 Sensor Bungs that use a M12 x 1.25 thread. This specific O2 sensor bung fitting features a hex head design for easy installation and removal. Our O2 sensor bungs and bung plugs are a high quality mild steel option for custom exhausts, downpipes, and OEM repair fabrication projects.